552 SMITH: DIOSCOREA VILLOSA 
cotyledon is tongue-shaped and not flattened. Bucherer also 
says that the primary root is endogenous and breaks through 
several rows of parenchyma cells when the seed germinates. No 
evidence of this condition has been found in D. villosa. There 
are no parenchyma layers outside the well-defined root-cap, which 
lies in immediate contact with the suspensor. 
: THE ENDOSPERM 
As has been said, the polar nuclei fuse early and the primary 
endosperm nucleus undergoes several divisions previous to the 
first division of the egg; the nuclear divisions in the endosperm 
are simultaneous. The young embryo is at all times closely 
invested with a thick layer of endosperm cytoplasm. The endo- 
sperm makes rapid inroads on the nucellar tissue, using up all of 
it excepting two layers at the sides of the embryo-sac cavity and 
thicker masses at the chalazal and micropylar ends before cell 
division begins in the endosperm. Cell formation in the endo- 
sperm begins when the embryo has reached about the stage shown 
in Fic. 10. Tissue is formed at first throughout the whole of the 
cavity; later, but before the maturing of the seed, enough of this 
tissue is dissolved to form a large fissure in the central part of the 
seed which affords room for the rapid growth of the cotyledon at 
the time of germination. The cells of the endosperm contain 
abundant reserves of hemicellulose, protein, and oil. Dutrochet 
(1835) and Beccari (18702) refer to the food material in the seeds 
of various Dioscoreaceae as ‘ perisperm,” but in Dioscorea villosa 
the material is clearly endosperm. 
Formation of endosperm tissue is accompanied by, and is 
perhaps responsible for, certain changes in the contour of the 
seed and in the position of the embrye. When cell walls begin 
to form in the endosperm, nuclear division continues and is 
especially active in the region opposite the funiculus and adjacent 
to the embryo with the final result that this portion of the seed 
becomes proportionately larger than the other parts. As a result 
of this one-sided growth, the embryo, whose long axis at first 
corresponds to the long axis of the embryo-sac, comes to lie with 
its axis at an angle of approximately forty-five degrees to the 
long axis of the seed. 
